1. Field of the Invention
The present invention relates to an image scanning method for automatically inspecting a product having light transmission regions, and an image scanning apparatus adapted to carry out such a method.
2. Description of the Related Art
An aperture grille, which is a color selecting mechanism used in, e.g., a picture tube known as Trinitron (trade name), is generally produced as illustrated in a schematic partial plan view of FIG. 1A and a partially enlarged longitudinal sectional view of FIG. 1B, wherein a band-shaped thin metal plate is etched successively like a blind to form slots 1 therein, and then it is finished to have a predetermined size. In FIG. 1A, a contour 3 of the aperture grille is denoted by a broken line.
It has been generally customary heretofore that whether the shape of the slots 1 in the aperture grille is within a standard range or not is decided by visual inspection or by measuring the transmittance of parallel light rays transmitted through the slots 1.
According to such a conventional inspection method, however, it is impossible to detect any small defects in the slots 1, although great defects may be detectable properly. Further, detection of any defect in the sectional shape of the aperture grille is extremely difficult.
There may be contrived another method for detection of defects in the slots 1 of the aperture grille by setting a light source and a camera fixedly, then passing the aperture grille through the space formed between the light source and the camera, and photographing the slots 1 of the aperture grille by the camera to thereby detect any defects. However, according to this method also, it is still difficult to find the defects since the amount of image data obtained by the camera is insufficient. And it is nearly impossible to detect any defective portion particularly in the sectional shape of the aperture grille.